(2005-) Sea snakes live in water, and even terrestrial snakes sometimes show swimming on water surface. In fact, the mechanism of snakes�f propulsion is almost same both in water and on ground. An amphibious snake-like robot ACM-R5 (Fig. 1) takes advantage of this fact. It can operate both on ground and in water undulating its long body (Fig. 2, Fig. 3).

    The joint of ACM-R5 consists of an universal joint and bellows (Fig 4). It was developed on the basis of the previous model HELIX, which was designed for research of spirochete-like helical swimming. An universal joint plays a role of bones, and bellows do a role of an integument. ACM-R5 can form a smooth shape due to this joint structure, and it is important for effective locomotion. To be precise, the universal joint has one passive twist joint at the intersection point of two bending axis to prevent mechanical interference with bellows.

    ACM-R5 is equipped with paddles and passive wheels around the body (Fig. 5). To generate propulsive force by undulation, the robot need a resistance property as it glides freely in tangential direction but cannot in normal direction. Due to the paddles and passive wheels, ACM-R5 obtains that character both in water and on ground.

    The control system of ACM-R5 is an advanced one. Each joint unit has CPU, battery, motors, so they can operate independently. Through communication lines each unit exchanges signals and automatically recognizes its number from the head, and how many units join the system. Thanks to this system operators can remove, add, and exchange units freely and they can operate ACM-R5 flexibly according to situations.

    ACM-R5 conducted demonstration in 2005 World Exposition, Aichi, Japan from June 9th to June 19th (Fig. 19). About 20-minute demonstration held 4 or 5 times per a day, and ACM-R5 was well received by visitors. During this period several units broke down by accident, but operators replaced and repaired them, and could keep the demonstration schedule.

    ACM-R5 is equipped with advanced control system and shows the ability of amphibious snake-like robots to a certain extent. However a large number of problems are remained for realization of practical snake-like robots, both in software and hardware.

References:

1. H. Yamada, S. Chigisaki, M. Mori, K. Takita, K. Ogami, S. Hirose; Development of Amphibious Snake-like Robot ACM-R5, The Proc. of 36th Int. Symposium on Robotics, TH3C4 (2005)